Skip to main content

Full text of "The water-culture method for growing plants without soil"

See other formats


CALIFORNIA AGRICULTURAL EXPERIMENT STATION 



C I R C U L.A'R 3 4 7 
Revised January 1950 



The Water-Culture 
Method for Growing 
Plants without Soil 



D. R. HOAGLAND and 

D. I. ARNON 

Revised by D. I. ARNON 



— — 



THIS EDITION includes a discussion 
of general principles underlying 
the use of ALL methods for growing 
plants without soil. 



THE COLLEGE OF AGRICULTURE 



UNIVERSITY OF CALIFORNIA 



BERKELEY 



ntttriCUlttttC is an all-inclusive term for the several methods of grow- 
ing plants in artificial media— water culture, aggregate culture, and the 
"adsorbed" nutrient technique. 

*=£? Most claims for the advantages of nutriculture are unfounded. 

< §Z It is not a new method for growing plants. 

^Z Anyone who uses it must have a knowledge of plant physiology. 

"§Z Its commercial application is justifiable under very limited conditions 
and only under expert supervision. 

<£? Nutriculture is rarely superior to soil culture: 

Yields are not strikingly different under comparable conditions. 

Plants cannot be spaced closer than in a rich soil. 

Plant growth habits are not changed by nutriculture. 

Water requirement is no less in nutriculture. 

Nutritional quality of the product is the same. 

Nutrient deficiencies, insect attacks, and diseases present similar problems. 

Climatic requirements are the same. 

Favorable air temperatures are just as necessary as in soil. 

-U -U -& 

If, realizing these limitations, you still wish to experiment with nutri- 
culture methods, you will find directions beginning on page 23. 

Type of container 23 

Nature of bed 24 

Aeration of the root system 26 

Planting procedures 27 

Managing the solutions 27 

Selecting the nutrient solution 29 

Preparing the nutrient solution 29 

Nutrient solutions for demonstrating mineral deficiencies 

in plants 31 



Foreword 



For over three decades, the California 
Agricultural Experiment Station has con- 
ducted investigations of problems of plant 
nutrition with the use of water-culture 
technique for growing plants, as one im- 
portant method of experimentation. The 
objective has been to gain a better under- 
standing of fundamental factors which 
govern plant growth, in order to deal 
more effectively with the many complex 
questions of soil and plant interrelations 
arising in the field. Many workers have 
participated in these investigations. One 
of them, Dr. W. F. Gericke, conceived the 
idea some time ago that the water-culture 
method, hitherto employed only for scien- 
tific studies, might be adapted to commer- 
cial use, and proceeded to devise special 
technique for this purpose. 

In the nineteen thirties, this develop- 
ment was given widespread publicity in 
newspapers, Sunday supplements, and 
popular journals. The possibility of 
growing plants in a medium other than 
soil intrigued many persons, and soon 
extravagant claims were being made by 
many of the most ardent proponents of 
the commercial use of the water-culture 
method. Furthermore, amateur garden- 
ers sought to make this method a new 
hobby. Thousands of inquiries came to 
the University of California for detailed 
information for general application of the 
water-culture method to commercial as 
well as to amateur gardening. 

Because of doubts expressed concern- 
ing many claims made for the use of the 
water-culture method as a means of crop 



production, it became evident that an in- 
dependent appraisal of this method of 
growing crops was highly desirable. I 
therefore requested Professors D. R. 
Hoagland and D. I. Arnon to conduct cer- 
tain additional investigations and to pre- 
pare a manuscript for a popular circular 
on the general subject of growing plants 
in nutrient solutions. 

When this circular was first published 
in 1938, neither the California Agricul- 
tural Experiment Station nor the authors 
made any general recommendations as to 
the use of soilless culture methods for 
commercial crop production. The pur- 
pose of the publication was to make avail- 
able such technical information from the 
researches of the Station to those who 
wished to experiment with the water- 
culture method on their own responsibil- 
ity. An attitude of caution and a balanced 
consideration of the various factors de- 
termining success in growing crops on a 
large scale, whether in soil or in nutrient 
solutions, was commended to the atten- 
tion of those contemplating commercial 
ventures. The purpose of this revised pub- 
lication and the point of view of the Ex- 
periment Station remain the same today. 
The experience of the past decade, during 
which a number of large-scale installa- 
tions for soilless crop production was 
established in the United States and over- 
seas, fails to support the exaggerated 
claims of the early enthusiasts of the 

technique. 

C. B. Hutchison 

Vice-President of the University and 
Dean of the College of Agriculture 



[3] 



THE WATER-CULTURE METHOD 
FOR GROWING PLANTS WITHOUT SOIL 

D. R. Hoagland and D. I. Arnon 
Revised by D. I. Arnon 2 



Nutriculture is the term applied to all 
methods for growing plants in a medium 
other than natural soil. It includes water 
culture, aggregate culture, and the "ad- 
sorbed-nutrient" technique, all of which 
are discussed briefly in this circular. Spe- 
cific directions, however, are given for 
water culture only. 

In the nineteen thirties, the popular 
press gave an immense amount of pub- 
licity to the subject of commercial or 
amateur growing of crops in "water cul- 
ture." This is a method of growing plants 
with their roots in a solution containing 
the mineral nutrients essential for plant 
growth. The solution takes the place of 
soil in supplying water and mineral nu- 
trients to the plant. "Tray agriculture," 
"tank farming," and "hydroponics," were 
other names given to this same process. 
Frequently, popular accounts left the im- 
pression that a new discovery had been 
made which would revolutionize present 
methods of crop production. Indeed, some 
predicted that in the future water culture 
would supplant the use of soils for grow- 
ing many crops and would thus produce 
far-reaching social dislocations. 

Extravagant claims for nutriculture 
are unfounded 

Promoters have made wholly un- 
founded claims that a new "profession of 
soilless farming" has been developed, af- 
fording extraordinary opportunities for 
investment of time and funds. They have 
attempted to convince the public that a 
short course of training will give prepara- 
tion for entering this new "profession." 
The impression has also been given that 
the water-culture method offers an easy 
means of raising food for household use. 



Widely circulated rumors, claims, and 
predictions about the water-culture pro- 
duction of crops often had little more to 
commend them than the author's unre- 
strained imagination. Grossly inaccurate 
in fact and misleading in implication, 
most of these claims betrayed an igno- 
rance of even the elementary principles of 
plant physiology. For example, there have 
been statements that in the future most 
of the food needed by the occupants of a 
great apartment building may be grown 
on the roof, and that in large cities "sky- 
scraper" farms may supply huge quanti- 
ties of fresh fruit and vegetables. One 
Sunday-supplement article contained an 
illustration showing a housewife opening 
a small closet off the kitchen and picking 
tomatoes from vines growing in water 
culture with the aid of electric lights. 
There has even arisen a rumor that the 
restaurants of a large chain in New York 
City are growing their vegetables in base- 
ments. Stories of this kind have gained 
wide currency and have captured the im- 
agination of many persons. 

Many factors have doubtless contrib- 
uted to arousing the surprisingly wide 
interest in the water-culture method of 
crop production. Current stress upon soil 
conservation, with attendant emphasis 
upon needless soil depletion and land 
erosion, has made the public especially 
receptive to new ideas relating to crop 
production. Some people have been im- 
pressed by the assumed social and eco- 
nomic significance of the water-culture 
method. Others, moved by the common 

1 Professor of Plant Nutrition and Plant Phys- 
iologist in the Experiment Station, deceased. 

2 Associate Professor of Plant Nutrition and 
Associate Plant Physiologist in the Experiment 
Station. 



[4] 



delight of mankind in growing plants, 
even though the garden space is reduced 
to a window sill, have sought directions to 
enable them to try a novel technique of 
plant culture. 

The consequence of the discussion of 
this method has been the creation of a 
great public demand for more specific 
information. Should this newly aroused 
interest in plant growth lead to a greater 
diffusion of the knowledge of certain 
general principles of plant physiology, 
the publicity regarding the water-culture 
method of crop production may in the 
long run have a beneficial effect. Growing 
plants in water culture has been consid- 
ered by some popular writers as a "mar- 
vel of science." The growth of plants is 
indeed marvelous, but not more so when 
plants are grown in water culture than 
when they are grown in soil. 

The two entirely distinct lines of in- 
vestigation at the California Agricultural 



Experiment Station, in which the water- 
culture technique is used, have sometimes 
been confused in popular discussions. 
One of these concerns methods of grow- 
ing plants in water culture under natural 
light; the other, the study of special scien- 
tific problems of plant growth in con- 
trolled chambers artificially illuminated. 
At the present time there is no economic 
possibility of growing commercial crops 
solely under artificial illumination, even 
if there were any reason for doing so. 

At several other institutions, consider- 
able attention has been devoted to a study 
of the effect of supplementing daylight 
with artificial light during some seasons 
of the year, to control the flowering period 
or to accelerate growth of certain kinds 
of plants (particularly floral) in green- 
houses. So far, this practice has been ap- 
plied mainly to plants developed in soil 
and has no essential relation to the water- 
culture method of growing plants. 



NUTRtCULWRE is not a new method 



Curiously enough, the earliest recorded 
experiment with water cultures was car- 
ried out in search of a so-called "principle 
of vegetation" in a day when so little was 
known about the principles of plant nu- 
trition that there was small chance of 
profitable results from such an experi- 
ment. Woodward (1699) grew spearmint 
in several kinds of water : rain, river, and 
conduit water, to which in one case he 
added garden mold. He found that the 
greatest increase in the weight of the 
plant took place in the water containing 
the greatest admixture of soil. He con- 
cluded "That earth, and not water, is the 
matter that constitutes vegetables." 

Water-culture technique developed 
from plant nutrition studies 

The real development of the technique 
of water culture took place over three- 
quarters of a century ago. It came as a 
logical result of the modern concepts of 
plant nutrition. By the middle of the 



nineteenth century, enough of the funda- 
mental facts of plant physiology became 
known and properly evaluated to enable 
the botanists and chemists of that period 
correctly to assign to soil the part it plays 
in the nutrition of plants. They realized 
that plants are made of chemical elements 
obtained from three sources: air, water, 
and soil, and that plants grow and in- 
crease in size and weight by combining 
these elements into various plant sub- 
stances. 

Water is, of course, always the main 
component of growing plants. But the 
major portion, usually about 90 per cent, 
of the dry matter of most plants is made 
up of three chemical elements: carbon, 
oxygen, and hydrogen. Carbon comes 
from the air, oxygen from the air and 
water, and hydrogen from water. In addi- 
tion to these three, plants contain other 
elements, such as nitrogen, phosphorous, 
potassium, and calcium, which they ob- 
tain from the soil. The soil then supplies 



[5] 



a large number of chemical elements, but 
they constitute only a very small portion 
of the plant. Yet the various elements that 
occur in plants in comparatively small 
amounts are just as essential to growth as 
those which compose the bulk of plant 
tissues. 

The publication in 1840 of Liebig's 
book on the application of organic chem- 
istry to agriculture and physiology, 3 in 
which these facts were ably and effec- 
tively brought to the attention of plant 
physiologists and chemists of that period, 
served as a great stimulus for undertaking 
experimental work in plant nutrition. 
(Liebig, however, failed to understand 
the role of soil as a source of nitrogen for 
plants; and the fixation of atmospheric 
nitrogen by bacteria was not then known. ) 

Once it was recognized that the func- 
tion of the soil in the economy of the 
plant is to furnish certain chemical ele- 
ments, as well as water, it was but natural 
to attempt to supply these elements and 
water independently of soil. The credit 
for initiating exact experimentation in 
this field belongs to the French chemist, 
Jean Boussingault, who is regarded as 
the founder of modern methods of con- 
ducting experiments in vegetation. 

Boussingault, who had begun his ex- 
periments on plants even before 1840, 
used insoluble artificial soils: sand, 
quartz, and sugar charcoal, which he 
watered with solutions of known com- 
position. His results provided experi- 
mental verification for the mineral theory 
of plant nutrition as put forward by 
Liebig, and were at once a demonstration 
of the feasibility of growing plants in a 
medium other than a "natural soil." 

This method of growing plants in arti- 
ficial insoluble soils was later improved 
by Salm-Horstmar (1856-1860) and has 
been used since, with technical improve- 
ments, by many investigators. In recent 
years, large-scale techniques have been 
devised for growing plants for experi- 
mental or commercial purposes in beds 
of sand or other inert solid material. 



Modern technique in water culture 
originated about 1860 

After they were successfully grown in 
artificial culture media, it was but one 
more step to dispense with any solid 
medium and attempt to grow plants in 
water to which were added the chemical 
elements they were known to require. 
This was successfully accomplished in 
1860 by Sachs and about the same time 
by Knop. To quote Sachs directly: 

In the year 1860, I published the results of 
experiments which demonstrated that land 
plants are capable of absorbing their nutritive 
matters out of watery solutions, without the aid 
of soil, and that it is possible in this way not 
only to maintain plants alive and growing for a 
long time, as had long been known, but also to 
bring about a vigorous increase of their organic 
substance, and even the production of seed 
capable of germination. 4 

The original technique developed by 
Sachs for growing plants in nutrient solu- 
tions is still widely used, essentially un- 
altered. He germinated the seed in 
well-washed sawdust, until the plants 
reached a size convenient for transplant- 
ing. After carefully removing and wash- 
ing the seedling, he fastened it into a 
perforated cork, with the roots dipping 
into the solution. The complete assembly 
is shown in figure 1, which is a reproduc- 
tion of Sachs' illustration. 

Since the publication of Sachs' stand- 
ard solution formula (table 1) for grow- 
ing plants in water culture, many other 
formulas have been used with success by 
investigators in different countries. Knop, 
who undertook water-culture experiments 
at the same time as Sachs, proposed in 
1865 a nutrient solution, which became 
one of the most widely employed in 
studies of plant nutrition. Other formulas 
for nutrient solutions have been proposed 
by Tollens in 1882, by Schimper in 1890, 
by Pfeffer in 1900, by Crone in 1902, by 

3 Liebig, Justus von. Chemistry in its applica- 
tions to agriculture and physiology. [English 
translation.] 401 pp. John Wiley, New York, 
N.Y. 1861. 

4 Sachs, Julius von. Lectures on the physiology 
of plants. 836 pp. Clarendon Press, Oxford. 1887. 



[6] 



Tottingham in 1914, by Shive in 1915, by 
Hoagland in 1920, and by many others. 
At the very beginning of the water- 
culture work, investigators clearly recog- 
nized that no one composition of a 
nutrient solution is always superior to 




Fig. 1. Water-culture 
installation employed 
by the plant physiologist 
Sachs in the middle of 
the last century. (Repro- 
duced from Sachs, Lec- 
tures on the Physiology 
of Plants, Clarendon 
Press. 1887.) 

every other composition, but that within 
certain ranges of composition and total 
concentration, there could be fairly wide 
latitude in the nutrient solutions suitable 
for plant growth. Thus Sachs wrote: 

I mention the quantities (of chemicals) I am 
accustomed to use generally in water cultures, 
with the remark, however, that a somewhat wide 
margin may be permitted with respect to the 
quantities of the individual salts and the con- 
centration of the whole solution — it does not 
matter if a little more or less of the one or the 
other salt is taken — if only the nutritive mixture 
is kept within certain limits as to quality and 
quantity, which are established by experience. 



Water culture was long used only 
as research technique 

Until recently, the water-culture tech- 
nique was employed exclusively in small- 
scale, controlled laboratory experiments 
intended to solve fundamental problems 
of plant nutrition and physiology. These 
experiments have led to the determination 
of the list of chemical elements essential 
for plant life. They have thus profoundly 
influenced the practice of soil manage- 
ment and fertilization for purposes of 
crop production. 5 In recent years, great 
refinements in water-culture technique 
have made possible the discovery of sev- 
eral new essential elements. These, al- 
though required by plants in exceedingly 
small amounts, often are of definite prac- 
tical importance in agricultural practice. 
The elements derived from the nutrient 
medium now considered to be indispen- 
sable for the growth of higher green 
plants are nitrogen, phosphorus, potas- 
sium, sulfur, calcium, magnesium, iron, 
boron, manganese, copper, and zinc. New 
evidence suggests that molybdenum has 
to be added to the list. 6 Present indica- 
tions are that further refinements of tech- 
nique may lead to the discovery of still 
other elements essential in minute quan- 
tity for growth. 

In addition to the list of essential ele- 
ments—obviously of first importance in 
making artificial culture media for grow- 
ing plants— a large amount of informa- 
tion has been amassed on the desirable 
proportions and concentrations of the 
essential elements, and on such physical 
and chemical properties of various cul- 
ture solutions as acidity, alkalinity, and 
osmotic characteristics. A most important 

5 However, nutrient solutions such as are em- 
ployed in water-culture experiments are not 
applied directly to soils. For discussion of fer- 
tilizer problems consult: Hoagland, D. R., 
Fertilizers, soil analysis, and plant nutrition. 
California Agr. Exp. Sta. Cir. 367: 1-24. Re- 
vised, 1949. 

6 Arnon, D. I., and P. R. Stout. Molybdenum 
as an essential element for higher plants. Plant 
Physiology 14: 599-602. 1939. 



[7] 



recent development in the technique has 
been the recognition of the importance, 
for many plants, of special aeration of 
the nutrient solution to supplement the 
oxygen supply normally entering it when 
in free contact with the surrounding at- 
mosphere. 

Present-day commercial water cul- 
ture involves no new principles 

The recently publicized use of the 
water-culture technique for commercial 
crop production rests on the same princi- 
ples of plant nutrition as were discussed 
above. It involves the application of a 
large-scale technique, developed on the 
basis of an understanding of plant nutri- 
tion gained in previous investigations 
conducted on a laboratory scale. The lat- 
ter have provided knowledge of the com- 
position of suitable culture solutions. 
Furthermore, methods of controlling the 
concentration of nutrients and the degree 
of acidity are, except for modifications 
imposed by the large scale of operations, 
similar to those employed in small-scale 
laboratory experiments. 

The selection of a particular type of 
covering for the tanks adapted to large- 
scale water-culture operations and of 
methods for supporting the plants de- 



pends on the kind of plant. Potatoes, for 
example, require a suitable bed in which 
tubers can develop. This is usually a 
porous one placed just above the level of 
the solution. Tomatoes need adequate 
support only for the aerial portion of the 
stem, assuming that the roots are in a 
favorable culture-solution medium, ade- 
quately aerated, and with light excluded. 
A porous bed may be convenient as a 
means of facilitating aeration of the solu- 
tion, as a heat insulator, or as a support 
for the plant, but plays no indispensable 
role. Aside from such considerations, the 
choice of a covering is determined largely 
by expense and convenience, provided the 
materials used are not toxic to plants. 

With any kind of covering for the 
tanks, an adequate supply of air to the 
roots must be provided. While the use of 
a porous bed instead of a perforated cover 
facilitates aeration of roots, the bed can 
be dispensed with if provision is made to 
bubble air through the nutrient solutions 
(fig. 2) . Recent experiments have shown 
that even with the use of a porous bed, 
bubbling air through the solution may be 
advantageous or, under some conditions, 
indispensable. 

As illustrations of some scientific prob- 
lems of plant nutrition which have been 



TABLE 1. — Composition of Nutrient Solutions Used by Early Investigators* t 



Sachs' solution 
(1860) 


Knop's solution 
(1865) 


Pfeffer's solution 
(1900) 


Crone's solution 
(1902) 


Ingredient 


Grams 

per 1,000 cc 

H2O 


Ingredient 


Grams 

per 1,000 cc 

H2O 


Ingredient 


Grams 

per 1,000 cc 

H2O 


Ingredient 


Grams 

per 1,000 cc 

H2O 


KN0 3 


1.00 


Ca(N0 3 ) 2 


0.8 


Ca(N0 3 ) 2 


0.8 


KN0 3 


1.00 


Ca 3 (P0 4 ) 2 


0.50 


KN0 3 


0.2 


KN0 3 


0.2 


Ca 3 (P0 4 ) 2 


0.25 


MgS0 4 


0.50 


KH 2 P0 4 


0.2 


MgS0 4 


0.2 


MgS0 4 


0.25 


CaS0 4 


0.50 


MgS0 4 


0.2 


KH 2 P0 4 


0.2 


CaS0 4 


0.25 


NaCl 


0.25 


FeP0 4 


Trace 


KC1 


0.2 


FeP0 4 


0.25 


FeS0 4 


Trace 






FeCl 3 


Small 
amount 







* These and other formulas are given in: Miller, E. C, Plant physiology, p. 195-97. McGraw-Hill Book Co., 
New York, N. Y. 1931. 

t For best results, these solutions should be supplemented with boron, manganese, zinc, copper, and 
molybdenum; see discussion in the text, pp. 29-31. 



[8] 




Fig. 2. The use of the water-culture technique 
for studying the nutritional responses of lettuce 
plants under controlled conditions. The indi- 
vidual plants are supported in corks, which are 
placed in holes drilled in the metal covers. The 
glass and rubber tubes carry compressed air, 
which is bubbled through the nutrient solution. 

elucidated by the aid of the water-culture 
method of experimentation, the effects of 
aeration of the roots on plant growth are 
shown in plate 1, A, and the foliage symp- 
toms of deficiencies of mineral elements 
required in large or minute quantity in 
plate 1, B and plates 2 to 4. 

Solid aggregate culture provides 
anchorage for plant roots 

In the water-culture technique the 
roots of plants are submerged in a liquid 
solution of plant nutrients. As in a soil, 
the roots serve as the organs of absorp- 
tion for water and nutrients; unlike in 
soil, the roots provide no anchorage for 
the aerial portions of the plant. Special 
provisions, discussed later, are necessary 
for supporting plants grown in water 
culture. 

Plants may be grown without soil, how- 
ever, by other techniques, in which the 
roots serve as organs of both absorption 
and anchorage. Instead of in a liquid 



medium, the plants are placed in some 
solid inert aggregate, periodically irri- 
gated by a synthetic nutrient solution. 
Sand culture is the earliest example of 
this technique. Its development paralleled 
that of water culture, and it was used 
by many investigators to study the same 
types of scientific problems of plant nu- 
trition as were discussed under water 
culture above. 

Several experiment stations in recent 
years have developed techniques of ag- 
gregate culture adapted to growing plants 
on a large scale. Instead of sand, many of 
these techniques make use of such coarser 
aggregates as gravel, cinders, burned 
shale (haydite), crushed granite, and 
vermiculite. These aggregates are placed 
in especially constructed beds to which 
the nutrient solutions are supplied at 
regular intervals. 

Subirrigation is often used in ag- 
gregate culture 

With the coarser aggregates, the nu- 
trient solution is generally supplied by 
a subirrigation method rather than by 
surface applications. Labor-saving, auto- 
matic devices for supplying nutrient so- 
lutions to the culture beds are usually a 
feature of the subirrigation methods. A 
detailed discussion of these procedures, 
which is beyond the scope of this circular, 
will be found in other publications. 7 

(The California Agricultural Experi- 
ment Station cannot provide copies of 
these publications. Inquiries should be 
made at the source.) 

7 Withrow, R. B., and Alice P. Withrow. Nutri- 
culture. Indiana (Purdue Univ.) Agric. Exp. 
Sta. S. C. 328: 1-60. 1948. 

Kiplinger, D. C, and Alex Laurie. Growing 
ornamental greenhouse crops in gravel culture. 
Ohio Agric. Exp. Sta. Research Bull. 679: 1-59. 
1948. 

Davidson, 0. W. Large-scale soilless culture 
for plant research. Soil Science 62: 71-86. 1946. 

Robbins, W. R. Growing plants in sand cul- 
tures for experimental work. Soil Science 62: 
3-22. 1946. 

Shive, J. W., and W. R. Robbins. Methods of 
growing plants in solution and sand cultures. 

New Jersey Agric. Exp. Sta. Bull. 636. 



[9] 



No new principles are used in com- 
mercial "aggregate" culture 

As with large-scale water culture, the 
techniques for aggregates do not rest on 
any newly discovered principles of plant 
nutrition. They represent an application 
of engineering and technical principles 
to the construction of beds and the cir- 
culation of the nutrient solution, with 
economy and ease in construction and 
operation as objectives. Ingenious as 
these technical devices are, they cannot 
assure success in growing plants to any 
operator who does not have a sound 
knowledge of the physiological and horti- 
cultural principles involved in crop pro- 
duction. These principles, which are the 
same for water and aggregate culture, 
will be referred to in subsequent sections 
of this circular. 

Adsorbed-nutrient technique does 
use a different principle 

With either aggregate or water culture, 
the plant nutrients are supplied in a 
chemical solution. The management of 
this solution involves the technical prob- 
lems of preparing, testing, and adjusting 
the concentrations of the individual nu- 
trients. 



Under the sponsorship of the Army 
Air Forces during World War II, the 
possibility of using a large-scale nutrient- 
culture technique which would have some 
of the "fool-proof" aspects of growing 
plants in a fertile soil was explored. In- 
stead of supplying the plant nutrients in 
repeated applications of nutrient so- 
lutions, as is the practice in aggregate 
culture, a different principle was used. 
The plant nutrients were not furnished as 
chemical salts but rather as "adsorbed 
ions" on synthetic ion-exchange mate- 
rials, in a manner similar to that in which 
some plant nutrients are bound to col- 
loids in natural soils. The "charged" ion- 
exchange materials were then mixed with 
sand prior to planting the crop. After the 
plants were in, only applications of water 
would be necessary to make growth pos- 
sible. 

These wartime experiments were prom- 
ising but were discontinued as the war 
ended, before the "adsorbed-nutrient" 
technique had passed the experimental 
stage. The information derived from these 
experiments has been published, 8 but no 
recommendations for commercial appli- 
cation can be made by the Experiment 
Station at this time. 



PRtHCfPLiS AND APPLICATION OF NUTRICULTURE 



A knowledge of plant physiology is 
necessary 

It should be stated at the outset that 
there is no magic in nutriculture methods. 
They provide only another means of sup- 
plying mineral nutrients and water to 
plants. The absorption of nutrients and 
water accounts for only two of the physio- 
logical processes of the plant. In order to 
evaluate the possibilities and limitations 
of any special technique for growing 
plants, one has to understand the signifi- 
cance of other interrelated processes, 
especially photosynthesis, respiration, 
transpiration, and reproduction. The 
currently prominent interest in the appli- 



cation of nutriculture techniques to crop 
production makes it desirable to discuss 
briefly the various factors which need to 
be considered by those contemplating an 
investment of time and funds in this field. 

What is the justification for nutri- 
culture in crop production? 

l.The answer to this question is that 
the method has certain possibilities in 

8 Arnon, Daniel I., and Karl A. Grossenbacher. 
Nutrient culture of crops with the use of syn- 
thetic ion-exchange materials. Soil Science 63: 
159-180. 1947. 

Arnon, Daniel I., and William R. Meagher. 
Factors influencing availability of plant nutri- 
ents from synthetic ion-exchange materials. Soil 
Science 64 : 213-221. 1947. 



[10 



the growing of special high-priced crops, 
particularly out of season in greenhouses, 
in localities where good soil is not avail- 
able, or when maintenance of highly 
favorable soil conditions is found too 
expensive. 

Soil beds in greenhouses often become 
infected with disease-producing organ- 
isms, or toxic substances may accumu- 
late. Installation of adequate equipment 
for sterilizing soils and operation of the 
equipment may require considerable ex- 
pense. Also, maintenance of fertility in 
the soil beds is often laborious and expen- 
sive. On the other hand, a synthetic nutri- 
ent medium, expertly supervised, can 
serve as a continuously favorable source 
of nutrients and water and, especially if 
combined with automatic devices, can 
bring about economies in labor. 

2. Very favorable climates in some re- 
gions may justify growing certain crops 
out of doors in nutriculture. The possi- 
bilities of nutriculture are not confined to 
greenhouses. In regions highly favored 
climatically and with a good water supply 
available, but where soil conditions are 
adverse, there may be reasons for grow- 
ing crops outdoors by nutriculture tech- 
niques. 

A case in point was the gravel-culture 
installation of the Army Air Forces on 
Ascension Island in the South Atlantic, 
toward the end of World War II. 9 This 
tiny volcanic island located near the 
equator has a climate characterized by 
mild temperatures and low rainfall. Over 
most of its area there is no agricultural 
soil. Because of the extreme geographic 
isolation and difficulties of supply, the 
large military garrison placed there dur- 
ing the war could be adequately provided 
only with the essential dietary staples, 
such as grains and meat and milk prod- 
ucts. The supply of fruits and vegetables 
was limited to canned, dried, or dehy- 
drated items. The psychological sat- 
isfactions from a supply of fresh salad 
vegetables and the attendant benefits to 
the morale and, in some cases, even to the 



health of troops, were deemed important 
enough to justify a determined effort to 
provide such items as fresh tomatoes, let- 
tuce, peppers, radishes, and cucumbers. 
To supply these from outside sources was 
not practical. To grow them on the island 
by conventional methods in soil was not 
feasible. An aggregate culture installa- 
tion, using a local gravel, was therefore 
authorized for the soilless production of 
fresh salad crops. 

A remarkable feature of the Ascension 
Island installation was the use of dis- 
tilled sea water in making the nutrient 
solutions. Without this engineering feat 
of providing by distillation the large 
water requirements of the growing crops, 
the project could not have been under- 
taken. The nutriculture installation on 
Ascension Island accomplished its mis- 
sion. It stands out as an example of the 
successful application of the principles 
of plant physiology and engineering tech- 
niques to the growing of crops in loca- 
tions devoid of natural soils. 

What are the drawbacks of com- 
mercial nutriculture? 

In the United States, nutriculture tech- 
niques have found application in green- 
houses in the production of floral and 
vegetable crops, and outdoors, in such 
climatically favorable areas as in Florida. 
Of the various techniques, the aggregate 
or gravel culture is the one most com- 
monly used in commercial installations. 
The commercial application of the nu- 
triculture techniques has not been as 
widespread as its most ardent followers 
expected. As foreseen over a decade ago 
in the first edition of this circular, two 
factors have limited the displacement of 
soil by nutriculture and will continue to 
do so : first, economic considerations and 
second, familiarity of commercial grow- 
ers with the management of soils rather 
than with nutriculture methods. 



Nutriculture. War Department Technical 
Manual TM 20-500. 



[HI 



1 . Nutriculture is costly and needs expert 
supervision. The initial financial invest- 
ment in nutriculture facilities is high. The 
automatic adjustment of many of the fac- 
tors determining the nutrition of the plant 
is found in a soil naturally fertile or in 
one capable of being made so by a simple 
treatment but is lacking in nutriculture 
methods. 

Expert supervision is generally neces- 
sary to cope with technical difficulties 
which may be met. Some of these are the 
character of the water, adjustment of the 
acidity of the nutrient solution, toxic sub- 
stances from tanks or beds, uncertainty 
as to time for replenishing salts in the 
nutrient solution or for changing it. 

To the average grower, crop pro- 
duction in nutriculture is an unfamiliar 
undertaking, involving problems not en- 
countered in soil culture. On the other 
hand, growing plants in soil is one of the 
oldest occupations of mankind, with a 
rich fund of accumulated experience to 
draw upon for guidance. 

In the absence of such special consid- 
erations which, for example, justified the 
operation of the Ascension Island installa- 
tion by the Army Air Forces during the 
war, commercial success is unlikely, un- 
less the most careful consideration is 
given to economic factors. What crops, if 
any, could be profitably grown by nutri- 
culture methods would depend on (1) the 
value of the crop in the market served, 
in relation to cost of production,— this 
would include a large outlay for beds, ma- 
terials, and other equipment— and (2) 
special costs of expert supervision and 
operation. 

2. Nutriculture demands knowledge of 
all factors of plant growth. Amateurs have 
sometimes mistakenly assumed that nutri- 
culture techniques can substitute for lack 
of horticultural skill in growing crops 
on a commercial scale. Indispensable to 
profitable crop production by nutricul- 
ture methods is a general knowledge of 
plant varieties, habits of growth, climatic 
adaptations, and pollination, and of the 



control of disease and insects— in other 
words, the same knowledge now needed 
for successful crop production in soils. 

Nutriculture does not solve prob- 
lems of sanitation 

In certain parts of the world, agricul- 
tural soils are fertilized by human ex- 
creta. Fresh vegetables from such areas, 
if consumed raw, are sometimes carriers 
of pathogenic organisms. It has been sug- 
gested that such a hazard can be elimi- 
nated by the use of outdoor nutriculture 
techniques. This suggestion does not 
seem to be supported by enough scientific 
evidence. It is not clear, for example, that 
outdoor installations will be protected 
from contamination by particles of soil, 
carried from adjoining infected areas by 
wind or other agencies. Rigorous cleans- 
ing of all vegetables to be consumed raw 
is a safety measure in any case. It is also 
possible that some suitable cleansing 
agent can be devised for the disinfection 
of soil-grown vegetables. Moreover, it has 
not been demonstrated that the disinfec- 
tion of selected local soil areas and the 
subsequent careful management of them 
are impractical or offer less health se- 
curity than artificial culture techniques. 

Wherever pathogenic organisms from 
the soil are a problem, standards of sani- 
tation are notoriously low. Handling vege- 
tables to be eaten raw, therefore, always 
constitutes a health hazard. Rigid sanita- 
tion measures are necessary against this 
source of infection, regardless of the 
method by which the crop was grown. 

Nutriculture is rarely superior to 
soil culture 

Yields are not strikingly different under 
comparable conditions. The impression 
conveyed by many of the popular discus- 
sions of nutriculture methods is that much 
more can be produced on a given surface 
of nutrient solution than on an equivalent 
surface soil, even under the best soil con- 
ditions feasible to maintain. Often quoted 
is the yield of tomato plants grown for a 



[12] 



»'- ■%» s^* ^ 5*"* * - r 




Fig. 3. Growth of tomato plants in fertile soil, in nutrient solution, and in pure silica 
sand irrigated each day with nutrient solution. Fruit had been harvested for 7 weeks 
prior to taking the photograph. All plants have made excellent growth and set large 
amounts of fruit in all three media. The general cultural conditions— spacing, staking, 
etc.— were the same. 



twelve months' period in a greenhouse 
water-culture experiment in Berkeley. 10 It 
is compared with average yields of toma- 
toes under ordinary field conditions; the 
yield from the water-culture plants is 
computed to be many times greater. But 
closer analysis shows that mistaken in- 
ferences may be drawn from this com- 



parison. Predictions concerning yields in 
large-scale production are of doubtful 
validity when based on those obtained in 
small-scale experiments under laboratory 
control. In any event, there is little profit 

10 Gericke, W. F. Crop Production without 
soil. Nature 141 : 536-40. 1938. See also the 
article cited in footnote 14, on page 19. 



[13] 



in comparing an average yield from un- 
slaked tomato plants, grown during a 
limited season under all types of soil and 
climatic conditions in the field, with that 
from staked plants grown in the protec- 
tion of a greenhouse for a full year. 

Evidence has long been available that 
yields of tomatoes grown in a greenhouse, 
in soil, can far exceed those obtained in 
the field. It is true that in one series of 
outdoor experiments, the yields of toma- 
toes under water-culture conditions were 
reported to be much higher than under 
ordinary field conditions; but again, the 
general cultural treatment of the plants— 
especially with regard to spacing and 
staking— was so different that compari- 
sons of yield do not mean very much. 

Any real test of the relative capacities 
of soil and nutriculture media for crop 
production requires that the two types of 
culture be carried on side by side, with 
similar spacing of plants and with the 
same cultural treatment otherwise. The 
soil should be of suitable depth and have 
its nutrient supplying power and physical 
condition as favorable for plant growth 
as possible. An experiment of this kind, 
with the tomato as the test plant, has been 
carried out in Berkeley. 11 Several conclu- 
sions derived from it warrant emphasis. 
The yield of tomatoes grown by the usual 
tank-culture technique was larger than 
any heretofore reported for this method. 
That from the soil-grown plants, however, 
was not markedly different (fig. 3) . When 
the greenhouse yields of tomatoes from 
either soil- or nutriculture-grown plants 
were compared on an acre basis with av- 
erage yields of field-grov;n tomatoes, the 
greenhouse plants gave far greater yields. 
Such comparisons, however, can have no 
direct practical significance because of 
the differences in climatic factors, cul- 
tural practice, and length of season in the 
greenhouse and in the open field. 

In one California commercial green- 
house, the yields of tomatoes grown in 
soil equaled those obtained in a success- 
ful commercial greenhouse using water 



culture. In another greenhouse using soil, 
the yields were larger. 

The yield of potatoes grown in a bed of 
peat soil in Berkeley was as large as any 
heretofore reported as produced by the 
water-culture method. 

Plants cannot be spaced closer than in 
a rich soil. The suggestion has sometimes 
been advanced that plants can be grown 
more closely spaced in nutrient solutions 
than in soil, but no convincing evidence of 
this has been given. In our experiments, 
we were able to grow tomato plants as 
close together in the soil as in the solu- 
tion (fig. 3) . The density of stand giving 
the highest yields would be determined by 
the adequacy of the light received by the 
plants, when growth is not limited by 
the supply of nutrients or water derived 
from either soil or nutrient solution. 
Closeness of spacing under field condi- 
tions is, of course, limited by practical 
considerations involving cost of crop 
production. This consideration of eco- 
nomic factors and of the adequacy of 
light does not justify the view that the 
nutriculture medium is better adapted 
than soil to growing several different 
crops simultaneously in the same bed. 

Plant growth habits are not changed by 
nutriculture. Some published pictures of 
tomato plants grown in nutriculture show 
impressive height. This growth in length 
of vines is frequently the subject of popu- 
lar comment. As a matter of fact, the 
ability of tomato vines to extend is char- 
acteristic of the plant and is not peculiar 
to the nutriculture method. Staked plants 
grown for a sufficiently long period in a 
fertile soil, under favorable light and 
temperature conditions, can also reach a 
great height and bear fruit at the upper 
levels (fig. 4) . In commercial greenhouse 
practice, growers usually "top" the vines. 
Fruit developed at higher level is likely 
to be of inferior quality and is relatively 

"Arnon, D. L, and D. R. Hoagland. Crop 
production in artificial culture solutions and in 
soils with special reference to factors influencing 
yields and absorption of inorganic nutrients. 
Soil Science 50 : 463-485. 1940. 



[14] 




•# ' \ 1*"* V -»' ""; ' V 






mm ^ 



f *if j ^M 



11 



Fig. 4. Under favorable conditions, tomato 
plants can grow to a great height and bear 
fruit over an extended period of time. This is 
equally possible in soil, sand, and water-culture 
media. The plants in the foreground were grown 
in a bed of fertile soil. At the time of taking this 
photograph, several days before the termina- 
tion of the experiment, most of the fruit had 
already been harvested. 

expensive to produce because of both the 
labor required to attach supports to the 
vines and the inconvenience of harvest- 
ing. Furthermore, it may become profit- 
able to discontinue the tomato harvest 
when prices become low in the summer 
and to use the greenhouse space to plant 
another crop for the winter harvest. 



Land plants have become adapted to 
growing in soils during their evolutionary 
history. It is not reasonable, therefore, to 
expect some extraordinary increase in 
their potentialities for growth when an 
artificial medium is substituted for soil. 
If no toxic conditions are present and a 
fully adequate supply of water, mineral 
salts, and oxygen is provided to the root 
system, either through an artificial nutri- 
ent solution or a soil, then in the absence 
of plant diseases and pests, the growth of 
a plant is limited by its inherited consti- 
tution and by climatic conditions. 

Water requirement is no less in nutri- 
culture. The view has sometimes been 
advanced that the water requirement is 
smaller in nutriculture than in soil. 
Utilizing climatically favored desert re- 
gions to produce crops by large-scale 
nutriculture is one of the recent popular 
misconceptions. Obviously, even if crops 
grown by this method in desert regions 
required less water, the difficulties in pro- 
viding a somewhat smaller supply for 
nutriculture would be essentially the same 
as those encountered in providing a 
larger amount for irrigation in soil. 
There is no direct evidence that crops 
produced by nutriculture require actually 
less water than those grown in soil, if 
the climatic conditions are the same. 

Tomatoes grown side by side in soil 
and in water culture in the same green- 
house 12 afforded an opportunity to meas- 
ure the relative amounts of water utilized. 
The numbers of gallons of water used to 
produce 100 pounds of fruit were as fol- 
lows: soil, 222; water culture, 257. These 
results indicate that somewhat more water 
was used to produce a unit weight of fruit 
under water culture than under soil con- 
ditions. What seems to warrant emphasis, 
however, is not the difference, but the 
essential similarity in the amount utilized 
by the plants grown in both media. This 
is in agreement with the fact that the prin- 
cipal use of water in producing a crop is 
through evaporation by the plant— a re- 

12 See footnote 11 on page 14. 



[15] 



quirement common to both soil and nutri- 
culture. The physiological characteristics 
of each species of plant, the extent of leaf 
surface, and the atmospheric conditions 
are the determining factors in this re- 
quirement. If a large crop is produced, 
either in nutriculture or in soil, and if 
climatic conditions favor high evapora- 
tion of water from the plant, the amount 
of water used in either case is necessarily 
large. 

Nutritional quality of the product is the 
same. Modern research on vitamins and 
on the role of mineral elements in animal 
nutrition has justly aroused great public 
interest. Here again much popular dis- 
cussion relating to their effect in diets 
and on health has been without scientific 
basis. It is, therefore, not unexpected that 
claims have been advanced for the superi- 
ority of food produced by nutriculture. 

As part of our investigation, careful 
studies of chemical composition and gen- 
eral quality have been made on tomatoes 
of several varieties grown in a fertile soil, 
and in sand- and water-culture media, 
side by side in the same greenhouse, with 
the same general cultural treatment. No 
significant difference has been discovered 
in the mineral content of the fruit de- 
veloped on plants grown in the several 
media. There is no scientific basis then 
for referring to tomatoes grown in nutri- 
culture as "mineralized." 

Among the minerals most frequently 
mentioned in this connection was calcium. 
It may be added, as a point of general 
interest, that all tomatoes, regardless of 
the method by which they were grown, 
contain but small amounts of calcium and 
are not therefore an important source of 
this mineral element in the diet. 

Tomatoes harvested from the soil and 
from water cultures could not be consist- 
ently distinguished in a test of flavor and 
general quality. 13 

No significant difference could be 
found in content of vitamins— carotene, 
or provitamin A, and vitamin C, in the 
fruit. 



Caution: No claims of unusual nutri- 
tional value for food products should be 
accepted unless they are supported by re- 
sults obtained in research institutes of 
high standing. 

The similarity in composition and gen- 
eral quality of the tomatoes grown in soil 
and water culture in the present experi- 
ments, may be explained by the facts that 
the climate and time of harvest were com- 
parable and that the supply of mineral 
nutrients was adequate in both cases. 
Whether plants are grown in soil or nu- 
triculture, climate and time of harvest 
are, of course, the factors that most affect 
quality and composition of plant product. 

Nutrient deficiencies, insect attacks, and 
diseases present similar problems. 

When plants are grown in solutions 
deficient in any of the nutrient ele- 
ments, symptoms appear, usually in the 
leaves. The series of photographs (plates 
2 to 4) shows the general character of 
foliage symptoms developed by the to- 
mato plant for each essential element 
omitted from experimental solutions. 

Nutriculture does not protect plants 
from any diseases except those strictly 
soil-borne. In fact, certain other diseases 
peculiar to water culture may sometimes 
attack them. 

The same insect pests attack plants 
grown in all media. 

Climatic requirements are the same. 
Many inquiries have been received on the 
possibility of growing plants in nutri- 
culture in dimly lighted places, or at low 
temperatures, under conditions which 
would prevent growth of plants in soil. 
Obviously, no nutrient solution can act 
as a substitute for light and suitable tem- 
perature. If there is doubt of the suita- 
bility of a particular location or season 
for the growth of any kind of plant, a 
preliminary experiment should be made 

13 The quality tests were conducted by Dr. 
Margaret Lee Maxwell Kleiber of the Division 
of Home Economics, and the carotene determi- 
nations were made by Dr. Gordon Mackinney of 
the Division of Food Technology, College of 
Agriculture. 



[16] 





Plate 1. A, B, Effect of forced aeration on asparagus plants grown in culture solutions: A, plants 
grown in solution through which air was bubbled continuously; B, plants without forced aeration. 

C, Asparagus plants grown in a nutrient solution in which boron, manganese/ zinc, and copper 
were present in such small amounts as one part in several million parts of solution; D, plants grown 
in solutions to which these elements were not added. 



by growing the plant in good garden soil. 
If the plant fails to make satisfactory 
development in the soil medium because 
of unfavorable light or temperature, fail- 
ure may also be expected under water- 
culture conditions. 



Sunlight and suitable temperatures are 
essential for green plants, in order that 
they may carry on one of the fundamental 
processes of plant growth, known as 
photosynthesis. In this process, the ele- 
ment carbon, which forms so large a 



[17] 




Plate 2. Symptoms of mineral deficiencies shown by tomato plants: A, complete 
nutrient solution; B, solution lacking nitrogen; C, solution lacking phosphorus; 
D, solution lacking potassium. 



part of all organic matter, is fixed by 
plants from the carbon dioxide of the 
atmosphere. This reaction requires a 
large amount of energy, which is ob- 
tained from sunlight. 

Plants depend on photosynthesis for 
their food, that is, for organic substances, 
such as carbohydrates, fats, and proteins, 



which provide them with energy and 
enter into the composition of plant sub- 
stance. The mineral nutrients absorbed 
by roots are indispensable for plant 
growth but do not supply energy and, in 
that sense, cannot be regarded as "plant 
food." 

Animal life is also absolutely dependent 



[18] 






i,!%- 







G H 

Plate 3. Symptoms of mineral deficiencies shown by tomato plants: E, solution 
lacking calcium; F, solution lacking sulfur; G, solution lacking magnesium; 
H, solution lacking boron. 



on this ability of the green plant to fix 
the energy of sunlight. 

Favorable air temperatures are just as 
necessary as in soil. An earlier report of 
a preliminary experiment by other in- 
vestigators suggested that under green- 
house conditions, heating the nutrient 
solution would produce large increases 
in the yield of tomatoes." This is not con- 
firmed by experiments we undertook in 
a Berkeley greenhouse, which was un- 



heated except on a few occasions to pre- 
vent temperatures from falling below 
50-55° Fahrenheit. Under the climatic 
conditions studied, the beneficial effects 
of heating the nutrient solution (to 70° F 
in the fall- winter and to 75° F in the 
spring-summer period) were not of sig- 
nificance. If favorable air temperatures 

14 Gericke, W. F., and J. R. Tavernetti. Heat- 
ing of liquid culture media for tomato produc- 
tion. Agricultural Engineering 17: 141-42, p. 
184. 1936. 



[19] 




Plate 4. Symptoms of mineral deficiencies shown by tomato plants: A, 
right, iron deficiency; left, complete nutrient solution; B, left, manganese 
deficiency; right, complete nutrient solution; C, left, copper deficiency; 
middle, complete nutrient solution; right, zinc deficiency; D, left, molyb- 
denum deficiency; right, complete nutrient solution. (Illustration from 
recent unpublished results of D. I. Arnon and P. R. Stout.) 



[20] 



are maintained, there seems to be no need 
to heat the solution. 

Attempts should not be made to guard 
against frost injury or unfavorable 
low air temperatures merely by heating 
the nutrient solution. .Proper provision 
should be made for direct heating of the 
greenhouse. This may be found desirable 
even when danger from low temperatures 
is absent, in order to control humidity 
and certain plant diseases. 

These experiments on tomatoes sug- 
gest that if greenhouse temperatures are 
properly controlled, the solution tempera- 
ture will take care of itself. Certainly no 
expense should be incurred for equip- 
ment for heating solutions, either in a 
greenhouse or outdoors, until experimen- 
tation has shown such heating to be 
profitable. 

There is no one best solution tempera- 
ture. The physiological effects of the 
temperature of the solution are inter- 
related with those of air temperature and 
of light conditions. 

Most amateurs who try the nutriculture 
method will grow plants in warm seasons 
and probably will not wish to complicate 
their installation by the addition of heat- 
ing devices. Anyone who desires to test 
the influence of heating the culture solu- 
tion should make comparisons of plants 
grown under exactly similar conditions, 
except for the difference of temperature 
in the solutions. 

Composition of nutrient solutions 
may vary 

No one nutrient solution is superior to all 
other solutions. Thousands of requests 
have been received by the Station for 
formulas for nutrient salt solutions. It is 
often supposed that some remarkable 
new combination of salts has been de- 
vised and that the prime requisite for 
growing crops in solutions is to use this 
formula. The fact is, there is no one com- 
position of a nutrient solution which is 
always superior to every other composi- 
tion. Plants have marked powers of adap- 



tation to different nutrient conditions. If 
this were not so, plants would not be 
growing in varied soils in nature. We 
have already emphasized that within cer- 
tain ranges of composition and total con- 
centration, fairly wide latitude exists in 
the preparation of nutrient solutions suit- 
able for plant growth. Many varied solu- 
tions have been used successfully by 
different investigators. Even when two 
solutions differ significantly in their 
effects on the growth of a particular kind 
of plant under a given climatic condition, 
the relation between the solutions will not 
necessarily be the same with another kind 
of plant, or with the same kind of plant 
under another climatic condition. 

Concentration of the solution changes 
as the plants grow. Another point con- 
cerning nutrient solutions needs to be 
stressed. After plants begin to grow, the 
composition of the nutrient solution 
changes because the constituents are ab- 
sorbed by plant roots. How rapidly the 
change occurs depends on the rate of 
growth of the plants and the volume of 
solution available for each plant. Even 
with large volumes of solutions, some 
constituents may become depleted in a 
comparatively short time by rapidly 
growing plants. This absorption of nu- 
trient salts causes not only a decrease in 
the total amounts of salts available, but 
a qualitative alteration as well, since not 
all the nutrient elements are absorbed at 
the same rates. One secondary result is 
that the acid-base balance (pH) of the 
solution may undergo changes which in 
turn may lead to the precipitation of 
certain essential chemical elements (par- 
ticularly, iron and manganese) so that 
they are no longer available to the plant. 
Also to be considered are the effects of 
salts added with the water (discussed 
later). 

Constant control of the solution is neces- 
sary. For these various reasons, the main- 
tenance of the most favorable nutrient 
medium throughout the life of the plant 
involves not merely the selection of an 



[21] 



appropriate solution at the time of plant- 
ing but also continued control, with either 
the addition of chemicals when needed 
or the replacement of the whole solution 
from time to time. Proper control of cul- 
ture solutions is best guided by observa- 
tions of the crop and by chemical analyses 
of samples of the solution taken periodi- 
cally. 

The objective of controlling the nutri- 
ent solutions is not to maintain a fixed 
composition of some "ideal" nutrient 
solution, but rather to provide the plant 
at each stage of its growth with a sufficient 
quantity of each essential element, within 
suitable ranges of total concentration and 
fairly broad limits of ionic proportions. 

Test tap water for salt content. For the 
purpose of exact control in his experi- 
ments, the plant physiologist prepares 
his solutions with distilled water. The 
commercial grower and the amateur are 
usually limited to the use of domestic or 
irrigation water, which contains various 
salts, including such sodium salts as 
sodium chloride, sodium sulfate, and 
sodium bicarbonate, as well as calcium 
and magnesium salts. 

Most waters suitable for irrigation or 
for drinking can be utilized in the water- 
culture method, but the adjustment of the 
reaction (pH) in the nutrient solution 
depends on the composition of the water. 
Some waters may be unfit for use in the 
solution because of high sodium salt con- 
tent. Even with a water only moderately 
high in it, the salt may concentrate in the 
nutrient solution with possible unfavor- 
able effects on the plant. This is particu- 
larly true when large amounts of water 
have to be added to the tanks and the 
solutions are not changed. In one in- 
stance, a well water was highly toxic be- 
cause it contained too high a concentration 
of zinc, apparently derived largely from 
circulation through galvanized pipes. 
This same water, however, was not in- 
jurious to tomato plants grown in soil 
because of the absorbing power of the 
soil for zinc. 



Nutrients cannot take the place of sun- 
shine. As already indicated, the successful 
growth of a crop is dependent on sunlight 
and temperature and humidity conditions, 
as well as on the supply of mineral nutri- 
ents furnished by the culture medium. 
Complex interrelations exist between cli- 
matic conditions and the utilization of 
these nutrients. The relation of nitrogen, 
nutrition, and climatic conditions to fruit- 
fulness has often been stressed. In some 
localities, deficient sunshine in winter 
months may limit the growth of many 
greenhouse crops, no matter what nutri- 
ent conditions are present in the culture 
solution. 

The same initial composition may supply 
nutrient requirements of many kinds of 
plants. The question is frequently asked: 
Does each kind of plant require a differ- 
ent kind of nutrient solution? The answer 
is that if proper measures are taken to 
provide an adequate supply of nutrient 
elements, then many kinds of plants can 
be grown successfully in nutrient solu- 
tions of the same initial composition. 
(The same fertile soil can produce high 
yields of many kinds of plants.) 

The composition of the nutrient solu- 
tion should always be considered in rela- 
tion to the total supply as well as to the 
proportions of the various nutrient ele- 
ments. To give a specific illustration: as- 
sume that several investigators prepare 
nutrient solutions of the same formula, 
but one uses 1 gallon of the solution for 
growing a certain number of plants, an- 
other 5 gallons of solution, and still an- 
other 50 gallons. If plants were grown to 
large size, each investigator would reach 
a different conclusion as to the adequacy 
of the nutrient solution employed, al- 
though the initial composition was the 
same in all cases. The investigator using 
the small volume might find that his 
plants became starved for certain nutri- 
ents, while the one using the larger vol- 
ume experienced no such difficulty. In 
fact, the precise initial composition of a 
culture solution has very little signifi- 



[22] 



cance, since the composition undergoes 
continuous change as the plant grows and 
absorbs nutrients. 

The rate and nature of this change de- 
pends on many factors, including total 
supply of nutrients. An adequate supply 
of nutrients involves (1) volume of solu- 
tion in relation to the number of plants 
grown, stage of growth of the plant, and 
rate of absorption of nutrients, and (2) 
frequency of changes of solution. 

Apart from the question of adequate 
supply of nutrients, certain special re- 
sponses of different species of plants have 
to be taken into account in the manage- 
ment of nutrient solutions. Plants vary 
in their tolerance to acidity and alkalin- 
ity. They also differ in their need for root 
aeration and in susceptibility to injury 
from excessive concentrations of ele- 
ments like boron, manganese, copper, 



and zinc. Some plants may be especially 
prone to yellowing because of difficulty 
in absorbing enough iron or manganese. 
Some may succeed best in a nutrient solu- 
tion more dilute than is employed for 
most kinds of plants. Unfavorable re- 
sponses by certain plants to high nitrogen 
supply in relation to fruiting, under cer- 
tain climatic conditions, may require con- 
sideration. 

Since the adaptation of a nutrient solu- 
tion to the growth of any particular kind 
of plant depends on the supply of nutri- 
ents and on climatic conditions, there is 
no possibility of prescribing a list of 
nutrient solutions, each one best for a 
given species of plant. 15 Some general 
type of solution, such as one of those 
described in this circular, should be tried 
first. It may be modified later by experi- 
ment if found necessary. 



DIRiCTtONS FOR THE water-culture method 



The preceding discussion dealt with 
general considerations bearing on the use 
of any soilless method of plant growth, 
especially by those who contemplate com- 
mercial ventures. What follows, deals with 
specific directions on how to proceed. 
These are given in response to numerous 
inquiries received from amateurs, pros- 
pective growers, teachers, and many 
others. As stated earlier, this circular 
describes only one technique for growing 
plants without soil, namely, the water- 
culture method. Other publications avail- 
able elsewhere (see footnote 7, page 9) 
give details of other techniques. 

The type of container 

The selection of a container depends 
on the kind of plant to be grown, the 
length of the growing period, and the 
purpose for which the plants are grown. 

In investigational work, 1- or 2-quart 
Mason jars provided with cork stoppers 
often serve as culture vessels (fig. 5). 



Sometimes 5- or 10-gallon earthenware 
jars are more suitable. Small tanks of 
various dimensions have been extensively 
used. For certain special investigations, 
shallow trays or vessels of Pyrex glass 
are required. Figure 6 shows the varied 
types of containers used at the Station 
for nutrient solutions in research prob- 
lems. 

For demonstrations in schools. Mason 
jars covered with brown paper to exclude 
light are excellent for demonstrations in 
schools (fig. 5). The jars should have 
cork stoppers in which one or more holes 
have been bored (sometimes a slit is also 
made in the cork ; see fig. 1 ) . Plants are 
fixed in the holes with cotton. Wheat or 
barley plants are very suitable for these 

15 A number of inquiries have been received 
regarding the culture of mushrooms. The water- 
culture method under discussion is unsuited to 
the culture of mushrooms. These plants require 
organic matter for their nutrition and differ in 
this way from green plants, which can grow 
in purely mineral nutrient solutions like those 
described in this circular. 



[23] 



demonstrations, since they may be grown 
in the jars without any special arrange- 
ments for aeration. 

For small-scale cultures. Two or 4- 
gallon crocks may be serviceable for 
small-scale cultures. Perforated corks 
fitting into specially constructed covers, 
or a porous bed of the kind described 
later, support the plants. Other useful 
containers are sheet metal tanks, such as 
those shown in figure 6. The dimensions 
of tanks are determined by the objective. 
A tank of moderate size, adapted to many 
purposes, is 30 inches long, 30 inches 
wide, and 8 inches deep (fig. 2, p. 9 and 
fig. 6, B) . A smaller one, 30 inches long, 
12 inches wide, and 8 inches deep, is con- 
venient for use in many experiments (fig. 
6, C) . In general, the tanks should be 
shallow, their length and width deter- 
mined by convenience and economy. 
They should have metal or wooden covers 
perforated to hold corks (fig. 6, A, C, 
D) which support the plants and in which 
the plants are fixed with cotton (fig. 2). 

For commercial water culture. For large- 
scale experimental installations or for 
commercial water culture, long, narrow, 
shallow tanks have been employed. They 
may be constructed of wood, cement, 
sheet metal, or other sufficiently cheap 
materials which do not give off toxic sub- 
stances. Wooden tanks must be made 
water tight. Redwood has been reported 
to give off toxic substances and, therefore, 
may require their removal by prelimi- 
nary leaching. Concrete tanks should 
also have thorough leaching before use. 
Caution: All tanks should be painted on 
the inside with asphalt or some other 
paint harmless to plants. Most ordinary 
paints cannot be used because of their 
toxic substances. Galvanized iron, even 
when coated with asphalt paint, may 
cause trouble if any of the paint scales 
off. Black iron tanks, well painted with 
asphalt (fig. 6, A) have proved satis- 
factory for experimental work. 

In experimental installations requiring 
large tanks, plants such as tomatoes were 




Fig. 5. Corn and sunflower plants grown in 
nutrient solution contained in 2-quart Mason 
jars. Note method of placing plants in perfo- 
rated corks. The jars are covered with thick 
paper to exclude light. 



supported in perforated cork, fitted into 
specially constructed metal covers. In 
commercial culture, however, a porous 
bed is commonly used. 

Nature of the bed 

Any good carpenter or mechanic can 
design and construct tanks and frames 
suitable for commercial nutriculture. 
Such installations generally consist of 
large tanks with porous beds for support- 
ing the plants. (In experimental work, 
the perforated cork often serves this pur- 
pose.) The beds in turn are supported by 
heavy chicken wire netting (1-inch mesh) 
coated with asphalt paint and stretched 
tightly across a frame that fits the top of 



[24] 



the container. This technique was first 
suggested by W. F. Gericke. 30 

Some suggestions for building the frame. 

1. The wire-netting must be stretched 
tightly across the frames and must be 
immediately above the surface of the solu- 
tion when the tank is full. 



are: pine excelsior, peat moss, pine shav- 
ings or sawdust, rice hulls. Certain mate- 
rials are toxic to plants. For this reason, 
redwood should usually be avoided. In 
experiments carried on in Berkeley with 
tomatoes, potatoes, and certain other 
plants, a layer of pine excelsior 2 or 3 




Fig. 6. Various types of containers for carrying on water-culture experiments: 

A, Large iron (not galvanized) tank painted inside with asphalt paint, outside 
with aluminum paint. Dimensions: 10 ft. x 2V2 ft. x 8 in. Shows one section of 
metal cover. Perforated corks for supporting plants are fixed in the holes (fig. 2). 
Wooden frames containing bedding material may also be set over these tanks, 
as shown in figure 7. 

B, Iron tank of dimensions: 30 in. x 30 in. x 8 in. 

C, Iron tank of dimensions: 30 in. x 12 in. x 8 in. 

D, Iron tank of dimensions: 15!/2 in. x IOV2 in. X 6 in. 

E, Graniteware pan 16 in. x 1 1 in. x 2V2 in. used for growing small plants. Per- 
forated metal covers, as shown in A, C, and D, may be used on all metal tanks 
or trays. The number of holes in the cover can be varied according to the number 
and size of plants to be grown. 

F and G, Pyrex dish and beaker used for special experiments designed to study 
the essentiality of certain chemical elements required by plants in minute quantity, 
such as zinc, copper, manganese, and molybdenum. The covers for these con- 
tainers, shown in the illustration, are molded from plaster of Paris and then 
coated with paraffin. 



2. Cross supports may be needed to 
keep the wire from sagging (fig. 7) . 

3. Several narrow sections of the frame 
may be left uncovered by wire and fitted 
with wooden covers instead. The latter 
may be removed easily for inspection of 
roots and for adding water or chemicals 
to the solution. 

Some porous materials that may be 
used. The layer of the porous material is 
generally 3 or 4 inches thick— thicker 
when tubers or fleshy roots develop in the 
bed. Some inexpensive bedding materials 



inches thick, with a superimposed layer 
of rice hulls about 1 or 2 inches thick, 
has produced no toxic effects. For plants 
that develop tubers or fleshy roots, some 
finer material may possibly need to be 
mixed with the excelsior. This is also 
essential when small seeds are planted in 

10 Gericke, W. F. Aquaculture : a means of 
crop production. American Journal of Botany 
16: 862. 1929. The general arrangement of this 
type of bed was described by: Gericke, W. F., 
and J. R. Tavernetti. Heating of liquid culture 
media for tomato production. Agricultural Engi- 
neering 17: 141^12, p. 184. 1936. 



[25] 



the bed to prevent their falling into the 
solution and to effect good contact of the 
moist material with the seed. In all cases 
the bed must be porous and permit free 
access of air. 

Care of the porous material. Seeds may 
be planted in the moist beds, or young 
plants from flats may be set in them with 



for plants differ greatly in this require- 
ment. In general, shallow, open tanks 
with porous beds facilitate aeration of 
the root system. It need not be assumed, 
however, that these beds assure the best 
growth for such plants as tomatoes, which 
have a high oxygen requirement. In one 
series of experiments, 17 tomato plants 




Fig. 7. General arrangement of tank equipment and method of planting: A, a 
frame supporting a wire screen fits over the metal tank (fig. 6, A) filled with the 
nutrient solution; B, tomato plants are placed with their roots immersed in 
the nutrient solution; a layer of excelsior is spread over the netting, as shown 
in the far end of the tank; C, the planting is completed by spreading a layer of 
rice hulls over the excelsior. 



their roots in the nutrient solution. When 
seeds are planted in the bed, they must 
of course be kept moist until the roots 
grow into the solution below. Occasional 
sprinkling will provide enough moisture 
for the development of tubers, bulbs, and 
fleshy roots. Great care should be ob- 
served to prevent waterlogging of the bed. 
This results from immersion of the lower 
portion of the bed in the solution and 
leads to exclusion of air and to undesir- 
able bacterial decompositions. 

Aeration of the root system 

In water culture, special attention has 
to be given to aeration of the root system, 



were grown in large shallow tanks pro- 
vided with porous beds, but without any 
special provision for aeration. A parallel 
culture was aerated by bubbling air 
through the solution. The latter showed a 
significant improvement in growth and 
yield, although the yields from the un- 
aerated beds were at least as large as any 
previously reported for this technique. 

Roots may develop in beds as well as 
in the solution, when porous beds are 
used. It has been suggested that for such 
plants as tomatoes, the additional roots in 
the bed may be essential for supplying 
certain factors required for the growth 

17 See footnote 11 on page 14. 



[26] 



of stem and for the prevention of chloro- 
sis. According to this hypothesis, even 
with adequate aeration, normal growth 
would be impossible if the roots were con- 
tinuously submerged in the nutrient solu- 
tion. No support for this hypothesis was 
found in an experiment with tomatoes in 
Berkeley. The plants were grown in metal 
tanks provided with metal covers, so con- 
structed that the level of the nutrient solu- 
tion was automatically maintained at the 
top of the tanks. When adequate aeration 
was provided, normal growth and devel- 
opment resulted without a porous bed 
and with the roots continuously sub- 
merged. 

Bubbling air through the solution. It is 
sometimes difficult to supply adequate 
oxygen when plants are grown in small 
containers and a large root system is to 
be developed. Bubbling air or circulating 
the solution is helpful in such cases. Va- 
rious devices, such as porous carbon 
pipes and glass tubes, can be used for 
this purpose. In general, too vigorous agi- 
tation of the solution should be avoided 
as it may harm tender roots. A continuous 
stream of small bubbles of air gives good 
results. Certain methods of circulating 
culture solutions not only bring about 
effective aeration but, in addition, equal- 
ize the supply of nutrients. Circulation of 
the nutrient solution from a central reser- 
voir was used successfully in one com- 
mercial greenhouse. For small scale or 
experimental installations, special devices 
for bubbling air or circulating the nutri- 
ent solution have been described. 18 

Planting procedures 

How to plant. Seeds may be planted 
directly in the moist bed. In that case, 
the whole bed must be installed and 
moistened before planting is begun. 

Other seeds— cereals, for example- 
may be germinated between layers of 
moist filter paper or paper toweling. This 
method is recommended if plants are to 
be fixed in corks and grown in jars or 
tanks with perforated metal or wooden 



covers. As soon as germination begins, 
the upper layer of moist paper is removed 
and the seedlings allowed to grow on the 
moist paper bed until they are large 
enough to be placed in corks. An excess 
of water is then added to the paper and 
the seedlings carefully removed without 
damage to the roots. 

Sometimes it is preferable to grow 
seeds in flats of good loam and then 
choose the most vigorous seedlings for 
transplanting into the bed. Just before 
transplanting, the soil must be thoroughly 
soaked with water so that the plants may 
be removed with the least possible injury 
to the roots. These should be rinsed free 
of the soil with a light stream of water 
and immediately set either in corks or in 
beds with the roots immersed in the solu- 
tion. In the latter case, the layer of excel- 
sior is built up over the wire screen as 
the roots are placed in the solution, and 
the layer of rice hulls is added last 
(%• 7). 

How to space plants. No general advice 
can be offered as to the best spacing. 
This depends on the kind of plant and on 
light conditions. Individual experience 
must guide the grower. In our experi- 
ments, tomato plants were set close to- 
gether, in some instances 20 plants to 25 
square feet of solution surface. 

Managing the solutions 

When to add water to tanks. In starting 
the culture, the tank is filled with solution 
almost to the level of the wire netting on 
the bottom of the bed. As they grow, the 
plants absorb water, or it evaporates from 
the surface of the solution, thus reducing 
its level in the tank. After the root system 
is sufficiently developed, this level is 
usually maintained from one to several 
inches below the lower part of the bed 
to facilitate aeration. Since the solution 

18 Furnstal, A. F., and S. B. Johnson. Prepara- 
tion of sintered Pyrex glass aerators for use in 
water-culture experiments with plants. Plant 
Physiology 11: 189-94. 1936. Compare also J. 
W. Shive and W. R. Robbins in the citation 
given in footnote 7, page 9. 



[27 



level should not be permitted to fall very 
far, however, water must be added at reg- 
ular intervals. 

As pointed out earlier, when large 
amounts of water have to be added, ex- 
cessive accumulations of certain salts 
contained in the water may occur. This 
is especially likely to happen if the salt 
content of the water is high. To avoid this 
difficulty, the entire solution is changed 
whenever the salt concentration becomes 
high enough to influence the plant ad- 
versely. Should plants be injured, how- 
ever, by the presence in the water of high 
concentrations of elements like zinc, 
changing solutions will not prevent in- 
jury. Because of the wide variation in the 
composition of water from different 
sources, no specific directions to cover 
all cases can be given. 

When to change the nutrient solution. 
As they begin to grow, the plants absorb 
the nutrient salts, thus causing the acidity 
of the solution to change. More salts and 
acid may be added. To know how much, 
requires chemical tests on the solution. 
When these cannot be made, an arbitrary 
procedure may be adopted of draining 
out the old solution every week or two, 
immediately refilling the tank with water 
and adding nutrients as at the beginning 
of the culture. The number of changes of 
solution required will depend on the size 
of plants, how fast they are growing, and 
on the volume of the solution. 

The nutrients should be distributed to 
different parts of the tank. To effect 
proper mixing, fill the tank at first only 
partly full (but keep most of the roots 
immersed), add the salts, and complete 
the filling to the proper level with a rapid 
stream of water, so directed as not to in- 
jure the roots. 

How to test and adjust acidity of water 
and nutrient solution. Ordinarily some 
latitude is permissible in the degree of 
acidity (pH) of the nutrient solution. For 
most plants, a moderately acid reaction 
(from pH 5.0 to 6.5) is suitable. If dis- 
tilled water is used in the preparation of 



nutrient solution, no adjustment of its 
reaction is necessary. If tap water is used, 
a preliminary test of its reaction should 
be made. Water found alkaline should be 
acidified before adding the nutrient salts. 
This should be done when the solution is 
first made up and at each subsequent 
change of solution. 

The chemicals required for testing 
acidity of water or nutrient solution are: 

1. Bromthymol blue indicator. This can 
be obtained, with directions for use, from 
chemical supply houses, in the form of 
solutions or impregnated strips of paper. 

Strips of other test papers covering a 
wide range of acidity are also now avail- 
able on the market. The amateur who 
understands their use will find them con- 
venient for adjusting the acidity of water 
as well as that of the nutrient solution. 

2. Sulfuric acid. Purchase a supply of 
3 per cent (by volume) acid of chemically 
pure grade. (Concentrated, chemically 
pure sulfuric acid may be purchased and 
diluted to 3 per cent strength, but the con- 
centrated acid is dangerous if handled 
by inexperienced persons.) This 3 per 
cent acid may be further diluted with 
water, if a preliminary test indicates the 
need of only small additions of acid. 

Test the degree of acidity of a measured 
sample of the water or nutrient solution 
(a quart, for example) by noting the 
color of the added indicator or test paper 
immersed in the solution. When bromthy- 
mol blue indicator is used, a yellow color 
indicates an acid reaction (with no 
further adjustment necessary) ; green, a 
neutral reaction ; blue, an alkaline one. 

If the original color is green or blue, 
add the dilute sulfuric acid (3 per cent 
or less in strength), slowly with stirring 
until the color just changes to yellow 
(indicating approximately pH 6). Do 
not add more beyond this point, since the 
yellow color will also persist when exces- 
sive amounts of acid are added. Record 
the amount of acid required. 

Finally, add a proportionate amount 
of the acid to the water or nutrient solu- 



[28] 



tion in the culture tank or vessel, having 
first determined how much it holds. 

Modification of the solution. Since con- 
siderable latitude is permissible in the 
composition of nutrient solution, analysis 
of tap water is not indispensable, unless 
the content of mineral matter is very high. 
Some waters may contain so much cal- 
cium, magnesium or sulfate, however, 
that further additions of these nutrient 
elements are unnecessary, or even un- 
desirable. As the objective should be to 
approximate the intended composition of 
the nutrient solution, taking into account 
the salt already present in the water, 
analysis of it is useful. 

Prepared salt mixtures not recom- 
mended. Many amateurs have become in- 
terested in the purchase of mixtures of 
nutrient salts ready for use. Various in- 
dividuals and firms have offered such 
mixtures for sale in small packages. 
Clearly a prepared salt mixture does not 
obviate the difficulties which may be met 
in growing plants in water culture. Re- 
cently, some firms have made highly mis- 
leading claims for the salt mixtures they 
sell. The Station makes no recommenda- 
tion with regard to any salt mixture. The 
fact that a mixture is registered with the 
California State Department of Agricul- 
ture, as required by the law governing 
sale of fertilizers, implies no endorsement 
for use of the product. The directions 
given later will, we hope, help the amateur 
to prepare his own nutrient solutions. 

Chemically pure salts commonly em- 
ployed in making nutrient solutions for 
scientific experiments would be too ex- 
pensive for commercial practice. A num- 
ber of ordinary fertilizer salts can serve 
in the production of crops by nutricul- 
ture methods. Recent developments in 
the fertilizer industry have made avail- 
able cheap salts of considerable degree 
of purity. Some commercial salts, how- 
ever, contain impurities (fluorine, for 
example, is commonly found in phosphate 
fertilizers) which may be toxic to plants 
under water-culture conditions. 



Selecting the nutrient solution 

As stated before, there is no one nutri- 
ent solution which is always superior to 
every other solution. Many solutions may 
be used with good results. Those de- 
scribed below have been found satisfac- 
tory with various species of plants in 
experiments conducted in Berkeley, with 
a source of good water. 

The composition of the solutions is 
given in two forms: (A) by rough meas- 
urements adapted to the amateur without 
special weighing or measuring instru- 
ments, and (B) in more exact terms for 
those with some knowledge of chemistry 
and the proper facilities for more ac- 
curate experimentation. These facilities 
would include chemical glassware, a 
chemical balance, and a supply of C.P. 
(chemically pure) chemicals. 

Preparing the nutrient solution 

Directions for amateurs. Either one of 
the solutions given in table 2 may be 
tried. Solution 2 may often be preferred 
because the ammonium salt delays the 
development of undesirable alkalinity. 
The salts are added to the water, prefer- 
ably in the order given. 

To either of the solutions, add the ele- 
ments iron, boron, manganese, and in 
some cases, zinc, and copper, which are 
required by plants in minute quantities. 
There is danger of toxic effects if much 
greater quantities of these elements are 
added than those indicated later in the 
text. Molybdenum and possibly other ele- 
ments required by plants in minute 
amounts will be furnished by impurities 
in the nutrient salts or in the water, and 
need not be added deliberately. 

a) Boron and Manganese Solution. 
Dissolve 3 teaspoons of powdered boric 
acid and 1 teaspoon of chemically pure 
manganese chloride (MnCl 2 • 4H 2 0) in 
a gallon of water. (Manganese sulfate 
could be substituted for the chloride.) 
Dilute 1 part of this solution with 2 parts 
of water, by volume. Use 1 pint of the 



[29 



diluted solution for each 25 gallons of 
nutrient solution. 

The elements in group a are added 
when the nutrient solution is first pre- 
pared and at all subsequent changes of 
solution. If plants develop symptoms 
characteristic of lack of manganese or 
boron (see plate 4, B, and plate 3, H) , 
solution a, in the amount indicated in the 
preceding paragraph, may be added be- 
tween changes of the nutrient solution or 
between addition of salts needed in large 
quantities. 10 But care is needed, for injury 
may easily be produced by adding too 
much of these elements. 

b) Zinc and Copper Solution. Ordi- 
narily this solution may be omitted, be- 
cause these elements will almost certainly 
be supplied as impurities in water or 
chemicals, or from the containers. When 
needed, (plate 4, C) additions are made 
as for solution a. To prepare solution b, 
dissolve 4 teaspoons of chemically pure 
zinc sulfate (ZnS0 4 • 7H 2 0) and 1 tea- 
spoon of chemically pure copper sulfate 



(CuS0 4 • 5H 2 0) in a gallon of water. 
Dilute 1 part of this solution with 4 parts 
of water. Use 1 teaspoon of the diluted 
solution for each 25 gallons of nutrient 
solution. 

c) Additions of Iron to Nutrient Solu- 
tion. Generally, iron solution will need to 
be added at frequent and regular inter- 
vals, perhaps as often as twice a week. If 
the leaves of the plant tend to become 
yellow (see plate 4, A) even more fre- 
quent additions may be required. A yel- 
lowing or mottling of leaves, however, 
can also arise from many other causes. 

The iron solution is prepared as fol- 
lows: Dissolve 1 level teaspoon of iron 
tartrate (iron citrate or iron sulfate can 
be substituted, but the tartrate or citrate 
is often more effective than the sulfate) 
in 1 quart of water. Add % cup of this 
solution to 25 gallons of nutrient solution 
each time iron is needed. 

10 The University is not prepared to diagnose 
symptoms on samples of plant tissues sent in 
for examination. 



TABLE 2. — Composition of Nutrient Solutions* 

(The amounts given are for 25 gallons of solution) 



Salt 



Grade 
of salt 



Approximate 
amount, 
in ounces 



Approximate 

amount, in 

level tablespoons 



Solution 1 f 






Potassium phosphate (monobasic) 

Potassium nitrate 


Technical 
Fertilizer 
Fertilizer 
Technical 


y 2 

2 
3 

V/2 


l 

4 (of powdered salt) 


Calcium nitrate 


7 


Magnesium sulfate (Epsom salt) 


4 



Solution 2f 






Ammonium phosphate (monobasic) 

Potassium nitrate 


Technical 
Fertilizer 
Fertilizer 
Technical 


V2 

2V 2 
2V 2 


2 

5 (of powdered salt) 


Calcium nitrate 


6 


Magnesium sulfate (Epsom salt) 


4 



* The University does not sell or give away any salts for growing plants in water culture. Chemicals may be 
purchased from local chemical supply houses, or possibly may be obtained through fertilizer dealers. Some of 
the chemicals may be obtained from druggists. If purchased in fairly large lots, the present price of the in- 
gredients contained in 1 pound of a complete mixture of nutrient salts is approximately 5 to 10 cents for either 
solution described above. 

f To either of these solutions, supplements of elements required in minute quantity must be added; see 
directions in the text. 



[30] 



Directions for schools or technical lab- 
oratories. For experimental purposes, the 
use of distilled water and chemically pure 
salts is recommended. Molar stock solu- 
tions (except when otherwise indicated) 
are prepared for each salt, and the 
amounts indicated below are used. 

Solution 1 ... , 

cc in a liter of 
nutrient solution 
M KH2PO4, potassium acid 

phosphate 1 

M KNO3, potassium nitrate 5 

M Ca(NOs) 2, calcium nitrate .. . 5 
M MgSCX, magnesium sulfate. . . 2 

Solution 2 . ... . 

cc in a liter of 
nutrient solution 

M NH4H2PO4, ammonium acid 

phosphate 1 

M KNOs, potassium nitrate 6 

M Ca(N0 3 )2, calcium nitrate ... 4 

M MgSCX, magnesium sulfate. . . 2 

To either of these solutions, add solu- 
tions a and b below. 

a) Prepare a supplementary solution 
which will supply boron, manganese, 
zinc, copper, and molybdenum, as fol- 
lows: 

Grams dissolved 
Compound in 1 liter of H 2 

H3BO3, boric acid 2.86 

MnCl 2 • 4H 2 0, manganese 

chloride 1.81 

ZnS0 4 • 7H2O, zinc sulfate 0.22 

CuSCX • 5H 2 0, copper sulfate. . 0.08 
H2M0O4 • H 2 0, molybdic acid 

(assaying 85 per cent M0O3) 0.02 

Add 1 cc of this solution for each liter 
of nutrient solution, when solution is first 
prepared or subsequently changed, or at 
more frequent intervals if necessary. 

This will give the following concen- 
trations : 

Parts per million of 
Element nutrient solution 

Boron 0.5 

Manganese 0.5 

Zinc 0.05 

Copper 0.02 

Molybdenum 0.01 

b) Add iron in the form of 0.5 per cent 
iron tartrate solution or other suitable 
iron salt, at the rate of 1 cc for each liter, 
about twice a week, or as indicated by 
appearance of plants. 

[31 



The reaction of the solution is adjusted 
to approximately pH 6 by adding 0.1 N 
H 2 S0 4 (or some other suitable dilution) . 

Molar Solutions. The concentrations 
of stock solutions of nutrient salts used 
in preparation of nutrient solutions are 
conveniently expressed in terms of mo- 
larity. A molar solution is one containing 
1 gram-molecule (mol) of dissolved sub- 
stance in 1 liter of solution. (In all 
nutrient-solution work, the solvent is 
water.) A gram-molecule or mol of a 
compound is the number of grams cor- 
responding to the molecular weight. 

Example 1, how to make a molar 
solution of magnesium sulfate: The mo- 
lecular weight of magnesium sulfate, 
MgS0 4 -7H 2 is 246.50. One mol of 
magnesium sulfate consists of 246.50 
grams. Hence, to make a molar solution 
of magnesium sulfate, dissolve 246.50 
grams of MgS0 4 ■ 7H 2 in water and 
make to 1 liter volume. 

Example 2, how to make a one-twentieth 
molar (0.05 M) solution of monocalcium 
phosphate, Ca(H 2 P0 4 ) 2 ■ H 2 (used in 
deficiency studies, below) : The molec- 
ular weight of monocalcium phosphate, 
Ca(H 2 P0 4 ) 2 • H 2 is 252.17. Hence 0.05 

252.17 grams 



molofCa(H 2 P0 4 ) 2 -H 2 Ois- 



20 



= 12.61 grams. Therefore, to make a 0.05 
M solution of monocalcium phosphate, 
dissolve 12.61 grams of Ca(H 2 P0 4 ) 2 # 
H 2 in water and make to 1 liter volume. 

Nutrient solutions for use in dem- 
onstrating mineral deficiencies 
in plants 

In any experiment to demonstrate min- 
eral deficiencies in plants, solution 1 or 
solution 2 should be used as a control to 
show normal growth in a complete solu- 
tion. Below are given six solutions, each 
lacking in one of the essential elements. 
Similar solutions were used in producing 
the deficiency symptoms shown in plates 
2 and 3, with plants which had previously 
been grown for several weeks in complete 
nutrient solutions. 



Distilled water should be used in mak- 
ing these solutions. 

cc in a liter of 
nutrient solution 

a, Solution lacking nitrogen 

0.5 M K 2 S0 4 5 

M MgS0 4 2 

0.05MCa(H 2 PO 4 ) 2 10 

0.01MCaSO 4 200 

b, Solution lacking potassium 

MCa(N03) 2 5 

M MgS0 4 2 

0.05MCa(H 2 PO 4 ) 2 10 

c, Solution lacking phosphorus 

MCa(N0 3 ) 2 4 

M KN0 3 6 

M MgS0 4 2 

d, Solution lacking calcium 

M KNO3 5 

M MgS0 4 2 

M KH 2 P0 4 1 

e, Solution lacking magnesium 

MCa(N0 3 ) 2 4 

M KNO3 6 

M KH 2 P0 4 1 

0.5 M K 2 S0 4 3 

/, Solution lacking sulfur 

MCa(N0 3 ) 2 4 

M KNO3 6 

M KH 2 P0 4 1 

MMg(N0 3 ) 2 2 



To any of these solutions, add iron and 
the supplementary solution supplying 
fjoron, manganese, zinc, copper, and 
molybdenum as previously described (p. 
29-31). For use with solution /, lacking 
sulfur, a special supplementary solution 
should be prepared in which chlorides 
replace the sulfates. Also, sulfuric acid 
should not be used in adjusting the re- 
action of the nutrient solution. 

In order to produce iron-deficiency 
symptoms, plants should be grown in 
glass containers; no iron should be added 
to the otherwise complete nutrient solu- 
tion. Similarly, it may be possible to 
produce boron- or manganese-deficiency 
symptoms with certain plants (tomatoes, 
for example) by omitting either one of 
these elements from the supplementary 
solution. Zinc-, copper-, and molybdenum- 
deficiency symptoms can usually be pro- 
duced only by the use of a special 
technique, the description of which was 
published in a technical paper. 20 

20 Stout, P. R., and D. I. Arnon. Experimental 
methods for the study of the role of copper, 
manganese, and zinc in the nutrition of higher 
plants. American Journal of Botany 26: 144-49. 



25m-l,'50(B7321) 



[32]